Preparation Of ZSM-5 Zeolite With Novel Organic Structure Directing Agent And Its Study On Catalytic Performance For Methanol To Aromatics

Light aromatics（benzene,toluene,xylene,BTX）are important basic organic chemical raw materials,and more than 97%of traditional aromatics production comes from petroleum raw materials.In recent years,due to the lack of domestic petroleum resources and the increase of aromatics demand,the traditional petroleum route has been difficult to meet the production demand.However,China’s methanol production capacity is seriously surplus,and the development of high value-added methanol downstream products is of great significance to the rational use of energy in China.Therefore,methanol to aromatics（MTA）has been attracted widespread attention for replacing traditional petroleum routes.Although China’s MTA technology has made great progress,low aromatics selectivity and high deactivation rate are still the main reasons limiting the industrialization of the process.Therefore,the preparation of catalysts with high aromatics selectivity and high stability is the key to the industrialization of MTA technology.In this paper,ZSM-5 zeolite was synthesized with different new organic structure directing agent,and compared with the ZSM-5 zeolite synthesized with tetrapropyl-ammonium hydroxide（TPAOH）as the template,the effects of different organic structure guides on the crystal morphology,acidity,pore structure,aluminum distribution and MTA reaction performance of the catalysts were studied.On this basis,the effects of silicon source,sodium content and sodium source on the reaction performance of ZSM-5 and MTA were investigated by using the best organic structure directing agent as template.Conclusions are as follows:1.ZSM-5 zeolite was not successfully prepared by using methylpropyl-piperidinium hydroxide（MPC₆）as an organic structure directing agent,which was mainly due to its weak structure directing effect.However,ZSM-5 zeolite was successfully prepared by using MPC₆ and TPAOH as the dual template.The results of MTA reaction showed that compared with ZSM-5 catalyst synthesized by TPAOH,ZSM-5 catalyst synthesized by MPC₆ and TPAOH showed a longer catalyst life of 41h,which was mainly due to fewer strong acid sites and higher mesoporous volume.2.ZSM-5 catalysts was successfully prepared by using butylmethyl-pyrrolidinium hydroxide（BMP）as a single template and BMP and TPAOH as dual templates.The acid properties,aluminum distribution and pore structure of ZSM-5 catalysts were obviously different between the two catalysts.The results of the MTA reaction showed that compared with the ZSM-5 catalyst synthesized by TPAOH,the stability of both catalysts was improved,and the catalyst lifetime was 57 h and 46 h,respectively,which was mainly due to the smaller number of strong acids and Bronsted acid sites.3.ZSM-5 catalyst was synthesized by using different silicon sources on the basis of BMP as template.The acidity,pore structure and aluminum distribution of ZSM-5catalysts prepared from different silicon sources were changed.The results of MTA reaction showed that the ZSM-5 catalyst synthesized by silica sol exhibited the most number strong and Bronsted acid sites,and the BTX selectivity is 36.8%.In addition,compared with other silicon sources,ZSM-5 catalyst synthesized by silica sol displayed lower average coke formation rate and better stability in MTA reaction.4.On the basis of BMP as template,Na⁺was introduced into the synthesis system,and the content of Na⁺and the type of sodium source were changed.The introduction of Na⁺changed the acidity and pore structure of the catalyst.Introduced appropriate amount of Na⁺had improved the acid site concentration and mesopore volume of the catalyst.The results of the MTA reaction showed that introduction of appropriate amount of Na⁺had improveed the selectivity of BTX and the higher catalyst stability was obtained,the highest BTX selectivity and catalyst lifetime were obtained when the Na⁺/Si ratio was 0.3,which were 44.3%and 77 h,respectively.The acidity and pore structure of the catalyst were obviously different when the sodium source was changed.The results of MTA reaction showed that the BTX selectivity of ZSM-5 catalyst was improved when Na Cl was used as the sodium source,which reached 37.8%.while The ZSM-5 catalyst synthesized with Na₂CO₃ had a slightly lower BTX selectivity,which is only 34.1%.